The invention relates to a power supply which includes at least one inverter whereto at least one voltage cascade (voltage multiplier) is connected, that is, notably a multi-phase cascade, in order to convert an input voltage applied to the input of the inverter into an output DC voltage (supply voltage), notably a high voltage for X-ray generators or rotating X-ray systems, for example, in computed tomography apparatus, or for single-tank generators. The invention also relates to a corresponding X-ray system.
X-ray systems generally include an X-ray source with an X-ray tube for generating X-rays, as well as an X-ray generator with a power supply (high-voltage generator) which includes a mains supply circuit and delivers the high voltage required for operation of the X-ray tube. When the X-ray source and the components generating the high voltage are combined so as to form one structural unit, such a unit is also referred to as a single tank generator.
For operation of X-ray tubes anode voltages of, for example, approximately 150 kV (in the case of single-pole power supply) or approximately +/−75 kV (in the case of double-pole power supply) are required between the anode and the cathode. Numerous requirements are imposed on these voltages or on the circuits whereby these voltages are generated. In order to avoid fluctuations of the X-ray intensity generated, the voltages should be as constant as possible and exhibit a low ripple only. In order to achieve this, an increasingly larger output capacitance is required for smoothing the voltages as the output powers increase at a given switching frequency of the inverter.
For fast control of the output voltage and the output current (for example, in the pulsed mode of the X-ray tube) and notably for fast reduction of the output voltage in the case of small currents, however, an as small as possible output capacitance is to be pursued; this output capacitance should also be as small as possible in order to limit the load for the X-ray tube in the case of a failure.
Furthermore, for application-specific or structural reasons (not elaborated herein) it may also be advantageous to utilize a single-pole supply voltage. The voltage of, for example, 150 kV to be realized in such a case imposes special requirements on the design of the high-voltage tank.
For the application in single-tank generators and in rotating X-ray systems, for example, as used in computed tomography apparatus (CT apparatus) a low weight and small volume are of special importance. These systems are notably those which operate at a rotary speed of several revolutions per second, for example, sub-second scanners in which centrifugal forces of 30 g or more may occur.
U.S. Pat. No. 4,995,069 discloses a power supply for an X-ray tube, notably for a CT apparatus, in which the alternating voltage present on the input is first rectified by means of a rectifier. In order to generate a double-pole supply voltage for the X-ray tube, for each pole a respective inverter for generating an alternating voltage is connected to the rectifier and a transformer for stepping up to the alternating voltage to an intermediate voltage is connected to the output of said inverter. For each pole the necessary anode or cathode voltage is then formed from these intermediate voltages by means of a voltage cascade. In order to save weight on the rotating part of the CT apparatus, the input voltage source, the rectifier, the inverter and the transformers are mounted on a stationary part, the secondary connections of the transformers being connected to the inputs of the voltage cascades via slip rings and slip contacts. However, this approach is considered to be detrimental, because the slip rings and slip contacts are subject to a comparatively high degree of wear, notably in the case of high numbers of revolution and/or high electric powers, and require frequent maintenance work
Therefore, it is an object of the invention to provide a power supply which is suitable notably for operation of an X-ray tube in a rotating X-ray system and has a particularly low weight and small volume in comparison with its output power.
It is also an object of the invention to provide a power supply of the kind set forth in which fast control of the output voltage and the output current is possible also for a high output power and a low ripple.
Finally, it is an object of the invention to provide a power supply which is also advantageously suitable for generating a single-pole supply voltage.